Trainer callbacks (#7596)

* Initial callback proposal

* Finish various callbacks

* Post-rebase conflicts

* Fix tests

* Don't use something that's not set

* Documentation

* Remove unwanted print.

* Document all models can work

* Add tests + small fixes

* Update docs/source/internal/trainer_utils.rst
Co-authored-by: Lysandre Debut <lysandre@huggingface.co>

* Address review comments

* Fix TF tests

* Real fix this time

* This one should work

* Fix typo

* Really fix typo
Co-authored-by: Lysandre Debut <lysandre@huggingface.co>

docs/source/index.rst

@@ -213,6 +213,7 @@ conversion utilities for the following models:
     :maxdepth: 2
     :caption: Main Classes
 
+    main_classes/callback
     main_classes/configuration
     main_classes/logging
     main_classes/model
@@ -270,3 +271,4 @@ conversion utilities for the following models:
     internal/modeling_utils
     internal/pipelines_utils
     internal/tokenization_utils
+    internal/trainer_utils

docs/source/internal/trainer_utils.rst

+Utilities for Trainer
+-----------------------------------------------------------------------------------------------------------------------
+
+This page lists all the utility functions used by :class:`~transformers.Trainer`.
+
+Most of those are only useful if you are studying the code of the Trainer in the library.
+
+Utilities
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. autoclass:: transformers.EvalPrediction
+
+.. autofunction:: transformers.set_seed
+
+.. autofunction:: transformers.torch_distributed_zero_first
+
+
+Callbacks internals
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. autoclass:: transformers.trainer_callback.CallbackHandler

docs/source/main_classes/callback.rst

+Callbacks
+-----------------------------------------------------------------------------------------------------------------------
+
+Callbacks are objects that can customize the behavior of the training loop in the PyTorch
+:class:`~transformers.Trainer` (this feature is not yet implemented in TensorFlow) that can inspect the training loop
+state (for progress reporting, logging on TensorBoard or other ML platforms...) and take decisions (like early
+stopping).
+
+Callbacks are "read only" pieces of code, apart from the :class:`~transformers.TrainerControl` object they return, they
+cannot change anything in the training loop. For customizations that require changes in the training loop, you should
+subclass :class:`~transformers.Trainer` and override the methods you need (see :doc:`trainer` for examples).
+
+By default a :class:`~transformers.Trainer` will use the following callbacks:
+
+- :class:`~transformers.DefaultFlowCallback` which handles the default beahvior for logging, saving and evaluation.
+- :class:`~transformers.PrinterCallback` or :class:`~transformers.ProrgressCallback` to display progress and print the
+  logs (the first one is used if you deactivate tqdm through the :class:`~transformers.TrainingArguments`, otherwise
+  it's the second one).
+- :class:`~transformers.integrations.TensorBoardCallback` if tensorboard is accessible (either through PyTorch >= 1.4
+  or tensorboardX).
+- :class:`~transformers.integrations.WandbCallback` if `wandb <https://www.wandb.com/>`__ is installed.
+- :class:`~transformers.integrations.CometCallback` if `comet_ml <https://www.comet.ml/site/>`__ is installed.
+
+The main class that implements callbacks is :class:`~transformers.TrainerCallback`. It gets the
+:class:`~transformers.TrainingArguments` used to instantiate the :class:`~transformers.Trainer`, can access that
+Trainer's internal state via :class:`~transformers.TrainerState`, and can take some actions on the training loop via
+:class:`~transformers.TrainerControl`.
+
+
+Available Callbacks
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Here is the list of the available :class:`~transformers.TrainerCallback` in the library:
+
+.. autoclass:: transformers.integrations.CometCallback
+    :members: setup
+
+.. autoclass:: transformers.DefaultFlowCallback
+
+.. autoclass:: transformers.PrinterCallback
+
+.. autoclass:: transformers.ProgressCallback
+
+.. autoclass:: transformers.integrations.TensorBoardCallback
+
+.. autoclass:: transformers.integrations.WandbCallback
+    :members: setup
+
+
+TrainerCallback
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. autoclass:: transformers.TrainerCallback
+    :members:
+
+
+TrainerState
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. autoclass:: transformers.TrainerState
+    :members:
+
+
+TrainerControl
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. autoclass:: transformers.TrainerControl
+    :members:

docs/source/main_classes/trainer.rst

@@ -18,7 +18,6 @@ previous features. To inject custom behavior you can subclass them and override
 - **get_eval_dataloader**/**get_eval_tfdataset** -- Creates the evaulation DataLoader (PyTorch) or TF Dataset.
 - **get_test_dataloader**/**get_test_tfdataset** -- Creates the test DataLoader (PyTorch) or TF Dataset.
 - **log** -- Logs information on the various objects watching training.
-- **setup_wandb** -- Setups wandb (see `here <https://docs.wandb.com/huggingface>`__ for more information).
 - **create_optimizer_and_scheduler** -- Setups the optimizer and learning rate scheduler if they were not passed at
   init.
 - **compute_loss** - Computes the loss on a batch of training inputs.
@@ -40,6 +39,10 @@ Here is an example of how to customize :class:`~transformers.Trainer` using a cu
             logits = outputs[0]
             return my_custom_loss(logits, labels)
 
+Another way to customize the training loop behavior for the PyTorch :class:`~transformers.Trainer` is to use
+:doc:`callbacks <callback>` that can inspect the training loop state (for progress reporting, logging on TensorBoard or
+other ML platforms...) and take decisions (like early stopping).
+
 
 Trainer
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@@ -47,29 +50,23 @@ Trainer
 .. autoclass:: transformers.Trainer
     :members:
 
+
 TFTrainer
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 .. autoclass:: transformers.TFTrainer
     :members:
 
+
 TrainingArguments
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 .. autoclass:: transformers.TrainingArguments
     :members:
 
+
 TFTrainingArguments
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 .. autoclass:: transformers.TFTrainingArguments
     :members:
-
-Utilities
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-
-.. autoclass:: transformers.EvalPrediction
-
-.. autofunction:: transformers.set_seed
-
-.. autofunction:: transformers.torch_distributed_zero_first

examples/seq2seq/seq2seq_trainer.py

@@ -9,7 +9,7 @@ from transformers import Trainer
 from transformers.configuration_fsmt import FSMTConfig
 from transformers.file_utils import is_torch_tpu_available
 from transformers.optimization import Adafactor, AdamW, get_linear_schedule_with_warmup
-from transformers.trainer import get_tpu_sampler
+from transformers.trainer_pt_utils import get_tpu_sampler
 
 
 try:

examples/seq2seq/test_finetune_trainer.py

@@ -4,7 +4,8 @@ import tempfile
 from unittest.mock import patch
 
 from transformers.testing_utils import slow
-from transformers.trainer_utils import TrainerState, set_seed
+from transformers.trainer_callback import TrainerState
+from transformers.trainer_utils import set_seed
 
 from .finetune_trainer import main
 from .test_seq2seq_examples import MBART_TINY

src/transformers/__init__.py

@@ -205,7 +205,15 @@ from .tokenization_xlm_roberta import XLMRobertaTokenizer
 from .tokenization_xlnet import SPIECE_UNDERLINE, XLNetTokenizer
 
 # Trainer
-from .trainer_utils import EvalPrediction, TrainerState, set_seed
+from .trainer_callback import (
+    DefaultFlowCallback,
+    PrinterCallback,
+    ProgressCallback,
+    TrainerCallback,
+    TrainerControl,
+    TrainerState,
+)
+from .trainer_utils import EvalPrediction, EvaluationStrategy, set_seed
 from .training_args import TrainingArguments
 from .training_args_tf import TFTrainingArguments
 from .utils import logging
@@ -529,7 +537,8 @@ if is_torch_available():
     from .tokenization_marian import MarianTokenizer
 
     # Trainer
-    from .trainer import EvalPrediction, Trainer, set_seed, torch_distributed_zero_first
+    from .trainer import Trainer
+    from .trainer_pt_utils import torch_distributed_zero_first
 else:
     from .utils.dummy_pt_objects import *
 

src/transformers/integrations.py

@@ -2,6 +2,11 @@
 import math
 import os
 
+from .file_utils import is_torch_tpu_available
+from .trainer_callback import TrainerCallback
+from .trainer_utils import PREFIX_CHECKPOINT_DIR, BestRun
+from .utils import logging
+
 
 try:
     import comet_ml  # noqa: F401
@@ -36,15 +41,6 @@ try:
 except (ImportError):
     _has_ray = False
 
-
-# No ML framework or transformer imports above this point
-
-from .trainer_utils import PREFIX_CHECKPOINT_DIR, BestRun  # isort:skip
-from .utils import logging  # isort:skip
-
-logger = logging.get_logger(__name__)
-
-
 try:
     from torch.utils.tensorboard import SummaryWriter  # noqa: F401
 
@@ -57,9 +53,10 @@ except ImportError:
     except ImportError:
         _has_tensorboard = False
 
-# Integration functions:
+logger = logging.get_logger(__name__)
 
 
+# Integration functions:
 def is_wandb_available():
     return _has_wandb
 
@@ -128,8 +125,8 @@ def run_hp_search_ray(trainer, n_trials: int, direction: str, **kwargs) -> BestR
 
     # The model and TensorBoard writer do not pickle so we have to remove them (if they exists)
     # while doing the ray hp search.
-    _tb_writer = trainer.tb_writer
-    trainer.tb_writer = None
+
+    _tb_writer = trainer.pop_callback(TensorBoardCallback)
     trainer.model = None
     # Setup default `resources_per_trial` and `reporter`.
     if "resources_per_trial" not in kwargs and trainer.args.n_gpu > 0:
@@ -182,5 +179,159 @@ def run_hp_search_ray(trainer, n_trials: int, direction: str, **kwargs) -> BestR
     analysis = ray.tune.run(_objective, config=trainer.hp_space(None), num_samples=n_trials, **kwargs)
     best_trial = analysis.get_best_trial(metric="objective", mode=direction[:3])
     best_run = BestRun(best_trial.trial_id, best_trial.last_result["objective"], best_trial.config)
-    trainer.tb_writer = _tb_writer
+    if _tb_writer is not None:
+        trainer.add_callback(_tb_writer)
     return best_run
+
+
+class TensorBoardCallback(TrainerCallback):
+    """
+    A :class:`~transformers.TrainerCallback` that sends the logs to `TensorBoard
+    <https://www.tensorflow.org/tensorboard>`__.
+
+    Args:
+        tb_writer (:obj:`SummaryWriter`, `optional`):
+            The writer to use. Will instatiate one if not set.
+    """
+
+    def __init__(self, tb_writer=None):
+        assert (
+            _has_tensorboard
+        ), "TensorBoardCallback requires tensorboard to be installed. Either update your PyTorch version or install tensorboardX."
+        self.tb_writer = tb_writer
+
+    def on_init_end(self, args, state, control, **kwargs):
+        if self.tb_writer is None and state.is_world_process_zero:
+            self.tb_writer = SummaryWriter(log_dir=args.logging_dir)
+
+    def on_train_begin(self, args, state, control, **kwargs):
+        if self.tb_writer is not None:
+            self.tb_writer.add_text("args", args.to_json_string())
+            self.tb_writer.add_hparams(args.to_sanitized_dict(), metric_dict={})
+
+    def on_log(self, args, state, control, logs=None, **kwargs):
+        if self.tb_writer:
+            for k, v in logs.items():
+                if isinstance(v, (int, float)):
+                    self.tb_writer.add_scalar(k, v, state.global_step)
+                else:
+                    logger.warning(
+                        "Trainer is attempting to log a value of "
+                        '"%s" of type %s for key "%s" as a scalar. '
+                        "This invocation of Tensorboard's writer.add_scalar() "
+                        "is incorrect so we dropped this attribute.",
+                        v,
+                        type(v),
+                        k,
+                    )
+            self.tb_writer.flush()
+
+    def on_train_end(self, args, state, control, **kwargs):
+        if self.tb_writer:
+            self.tb_writer.close()
+
+
+class WandbCallback(TrainerCallback):
+    """
+    A :class:`~transformers.TrainerCallback` that sends the logs to `Weight and Biases
+    <https://www.wandb.com/>`__.
+    """
+
+    def __init__(self):
+        assert _has_wandb, "WandbCallback requires wandb to be installed. Run `pip install wandb`."
+        self._initialized = False
+
+    def setup(self, args, state, model):
+        """
+        Setup the optional Weights & Biases (`wandb`) integration.
+
+        One can subclass and override this method to customize the setup if needed. Find more information
+        `here <https://docs.wandb.com/huggingface>`__. You can also override the following environment variables:
+
+        Environment:
+            WANDB_WATCH (:obj:`str`, `optional` defaults to :obj:`"gradients"`):
+                Can be :obj:`"gradients"`, :obj:`"all"` or :obj:`"false"`. Set to :obj:`"false"` to disable gradient
+                logging or :obj:`"all"` to log gradients and parameters.
+            WANDB_PROJECT (:obj:`str`, `optional`, defaults to :obj:`"huggingface"`):
+                Set this to a custom string to store results in a different project.
+            WANDB_DISABLED (:obj:`bool`, `optional`, defaults to :obj:`False`):
+                Whether or not to disable wandb entirely.
+        """
+        self._initialized = True
+        if state.is_world_process_zero:
+            logger.info(
+                'Automatic Weights & Biases logging enabled, to disable set os.environ["WANDB_DISABLED"] = "true"'
+            )
+            combined_dict = {**args.to_sanitized_dict()}
+            if hasattr(model, "config"):
+                combined_dict = {**model.config.to_dict(), **combined_dict}
+            wandb.init(project=os.getenv("WANDB_PROJECT", "huggingface"), config=combined_dict, name=args.run_name)
+            # keep track of model topology and gradients, unsupported on TPU
+            if not is_torch_tpu_available() and os.getenv("WANDB_WATCH") != "false":
+                wandb.watch(model, log=os.getenv("WANDB_WATCH", "gradients"), log_freq=max(100, args.logging_steps))
+
+    def on_train_begin(self, args, state, control, model=None, **kwargs):
+        if not self._initialized:
+            self.setup(args, state, model)
+
+    def on_log(self, args, state, control, model=None, logs=None, **kwargs):
+        if not self._initialized:
+            self.setup(args, state, model)
+        if state.is_world_process_zero:
+            wandb.log(logs, step=state.global_step)
+
+
+class CometCallback(TrainerCallback):
+    """
+    A :class:`~transformers.TrainerCallback` that sends the logs to `Comet ML
+    <https://www.comet.ml/site/>`__.
+    """
+
+    def __init__(self):
+        assert _has_comet, "CometCallback requires comet-ml to be installed. Run `pip install comet-ml`."
+        self._initialized = False
+
+    def setup(self, args, state, model):
+        """
+        Setup the optional Comet.ml integration.
+
+        Environment:
+            COMET_MODE (:obj:`str`, `optional`):
+                "OFFLINE", "ONLINE", or "DISABLED"
+            COMET_PROJECT_NAME (:obj:`str`, `optional`):
+                Comet.ml project name for experiments
+            COMET_OFFLINE_DIRECTORY (:obj:`str`, `optional`):
+                Folder to use for saving offline experiments when :obj:`COMET_MODE` is "OFFLINE"
+
+        For a number of configurable items in the environment,
+        see `here <https://www.comet.ml/docs/python-sdk/advanced/#comet-configuration-variables>`__.
+        """
+        self._initialized = True
+        if state.is_world_process_zero:
+            comet_mode = os.getenv("COMET_MODE", "ONLINE").upper()
+            args = {"project_name": os.getenv("COMET_PROJECT_NAME", "huggingface")}
+            experiment = None
+            if comet_mode == "ONLINE":
+                experiment = comet_ml.Experiment(**args)
+                logger.info("Automatic Comet.ml online logging enabled")
+            elif comet_mode == "OFFLINE":
+                args["offline_directory"] = os.getenv("COMET_OFFLINE_DIRECTORY", "./")
+                experiment = comet_ml.OfflineExperiment(**args)
+                logger.info("Automatic Comet.ml offline logging enabled; use `comet upload` when finished")
+            if experiment is not None:
+                experiment._set_model_graph(model, framework="transformers")
+                experiment._log_parameters(args, prefix="args/", framework="transformers")
+                if hasattr(model, "config"):
+                    experiment._log_parameters(model.config, prefix="config/", framework="transformers")
+
+    def on_train_begin(self, args, state, control, model=None, **kwargs):
+        if not self._initialized:
+            self.setup(args, state, model)
+
+    def on_log(self, args, state, control, model=None, logs=None, **kwargs):
+        if not self._initialized:
+            self.setup(args, state, model)
+        if state.is_world_process_zero:
+            experiment = comet_ml.config.get_global_experiment()
+            if experiment is not None:
+                experiment._log_metrics(logs, step=state.global_step, epoch=state.epoch, framework="transformers")

src/transformers/trainer.py

+# coding=utf-8
+# Copyright 2020-present the HuggingFace Inc. team.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+"""
+The Trainer class, to easily train a 🤗 Transformers from scratch or finetune it on a new task.
+"""
+
 import inspect
-import math
 import os
 import re
 import shutil
 import warnings
-from contextlib import contextmanager
 from pathlib import Path
 from typing import Any, Callable, Dict, List, Optional, Tuple, Union
 
@@ -15,8 +31,7 @@ from torch import nn
 from torch.utils.data.dataloader import DataLoader
 from torch.utils.data.dataset import Dataset
 from torch.utils.data.distributed import DistributedSampler
-from torch.utils.data.sampler import RandomSampler, Sampler, SequentialSampler
-from tqdm.auto import tqdm, trange
+from torch.utils.data.sampler import RandomSampler, SequentialSampler
 
 from .data.data_collator import DataCollator, DataCollatorWithPadding, default_data_collator
 from .file_utils import WEIGHTS_NAME, is_datasets_available, is_torch_tpu_available
@@ -34,23 +49,35 @@ from .modeling_auto import MODEL_FOR_QUESTION_ANSWERING_MAPPING
 from .modeling_utils import PreTrainedModel
 from .optimization import AdamW, get_linear_schedule_with_warmup
 from .tokenization_utils_base import PreTrainedTokenizerBase
+from .trainer_callback import (
+    CallbackHandler,
+    DefaultFlowCallback,
+    PrinterCallback,
+    ProgressCallback,
+    TrainerCallback,
+    TrainerControl,
+    TrainerState,
+)
+from .trainer_pt_utils import (
+    SequentialDistributedSampler,
+    distributed_broadcast_scalars,
+    distributed_concat,
+    get_tpu_sampler,
+    nested_concat,
+    nested_detach,
+    nested_numpify,
+    nested_xla_mesh_reduce,
+    reissue_pt_warnings,
+)
 from .trainer_utils import (
     PREFIX_CHECKPOINT_DIR,
     BestRun,
     EvalPrediction,
-    EvaluationStrategy,
     HPSearchBackend,
     PredictionOutput,
-    TrainerState,
     TrainOutput,
     default_compute_objective,
     default_hp_space,
-    distributed_broadcast_scalars,
-    distributed_concat,
-    nested_concat,
-    nested_detach,
-    nested_numpify,
-    nested_xla_mesh_reduce,
     set_seed,
 )
 from .training_args import TrainingArguments
@@ -60,7 +87,8 @@ from .utils import logging
 _use_native_amp = False
 _use_apex = False
 
-PT_LR_SCHEDULER_WARNING = "Please also save or load the state of the optimzer when saving or loading the scheduler."
+DEFAULT_CALLBACKS = [DefaultFlowCallback]
+
 
 # Check if Pytorch version >= 1.6 to switch between Native AMP and Apex
 if version.parse(torch.__version__) < version.parse("1.6"):
@@ -82,16 +110,20 @@ if is_torch_tpu_available():
     import torch_xla.distributed.parallel_loader as pl
 
 if is_tensorboard_available():
-    try:
-        from torch.utils.tensorboard import SummaryWriter
-    except ImportError:
-        from tensorboardX import SummaryWriter
+    from .integrations import TensorBoardCallback
+
+    DEFAULT_CALLBACKS.append(TensorBoardCallback)
+
 
 if is_wandb_available():
-    import wandb
+    from .integrations import WandbCallback
+
+    DEFAULT_CALLBACKS.append(WandbCallback)
 
 if is_comet_available():
-    import comet_ml
+    from .integrations import CometCallback
+
+    DEFAULT_CALLBACKS.append(CometCallback)
 
 if is_optuna_available():
     import optuna
@@ -102,91 +134,20 @@ if is_ray_available():
 logger = logging.get_logger(__name__)
 
 
-def reissue_pt_warnings(caught_warnings):
-    # Reissue warnings that are not the PT_LR_SCHEDULER_WARNING
-    if len(caught_warnings) > 1:
-        for w in caught_warnings:
-            if w.category != UserWarning or w.message != PT_LR_SCHEDULER_WARNING:
-                warnings.warn(w.message, w.category)
-
-
-@contextmanager
-def torch_distributed_zero_first(local_rank: int):
-    """
-    Decorator to make all processes in distributed training wait for each local_master to do something.
-
-    Args:
-        local_rank (:obj:`int`): The rank of the local process.
-    """
-    if local_rank not in [-1, 0]:
-        torch.distributed.barrier()
-    yield
-    if local_rank == 0:
-        torch.distributed.barrier()
-
-
-class SequentialDistributedSampler(Sampler):
-    """
-    Distributed Sampler that subsamples indicies sequentially,
-    making it easier to collate all results at the end.
-
-    Even though we only use this sampler for eval and predict (no training),
-    which means that the model params won't have to be synced (i.e. will not hang
-    for synchronization even if varied number of forward passes), we still add extra
-    samples to the sampler to make it evenly divisible (like in `DistributedSampler`)
-    to make it easy to `gather` or `reduce` resulting tensors at the end of the loop.
-    """
-
-    def __init__(self, dataset, num_replicas=None, rank=None):
-        if num_replicas is None:
-            if not torch.distributed.is_available():
-                raise RuntimeError("Requires distributed package to be available")
-            num_replicas = torch.distributed.get_world_size()
-        if rank is None:
-            if not torch.distributed.is_available():
-                raise RuntimeError("Requires distributed package to be available")
-            rank = torch.distributed.get_rank()
-        self.dataset = dataset
-        self.num_replicas = num_replicas
-        self.rank = rank
-        self.num_samples = int(math.ceil(len(self.dataset) * 1.0 / self.num_replicas))
-        self.total_size = self.num_samples * self.num_replicas
-
-    def __iter__(self):
-        indices = list(range(len(self.dataset)))
-
-        # add extra samples to make it evenly divisible
-        indices += indices[: (self.total_size - len(indices))]
-        assert (
-            len(indices) == self.total_size
-        ), f"Indices length {len(indices)} and total size {self.total_size} mismatched"
-
-        # subsample
-        indices = indices[self.rank * self.num_samples : (self.rank + 1) * self.num_samples]
-        assert (
-            len(indices) == self.num_samples
-        ), f"Indices length {len(indices)} and sample number {self.num_samples} mismatched"
-
-        return iter(indices)
-
-    def __len__(self):
-        return self.num_samples
-
-
-def get_tpu_sampler(dataset: Dataset):
-    if xm.xrt_world_size() <= 1:
-        return RandomSampler(dataset)
-    return DistributedSampler(dataset, num_replicas=xm.xrt_world_size(), rank=xm.get_ordinal())
-
-
 class Trainer:
     """
     Trainer is a simple but feature-complete training and eval loop for PyTorch,
     optimized for 🤗 Transformers.
 
     Args:
-        model (:class:`~transformers.PreTrainedModel`, `optional`):
+        model (:class:`~transformers.PreTrainedModel` or :obj:`torch.nn.Module`, `optional`):
             The model to train, evaluate or use for predictions. If not provided, a ``model_init`` must be passed.
+
+            .. note::
+
+                :class:`~transformers.Trainer` is optimized to work with the :class:`~transformers.PreTrainedModel`
+                provided by the library. You can still use your own models defined as :obj:`torch.nn.Module` as long as
+                they work the same way as the 🤗 Transformers models.
         args (:class:`~transformers.TrainingArguments`, `optional`):
             The arguments to tweak for training. Will default to a basic instance of :class:`~transformers.TrainingArguments`
             with the ``output_dir`` set to a directory named `tmp_trainer` in the current directory if not provided.
@@ -210,8 +171,11 @@ class Trainer:
         compute_metrics (:obj:`Callable[[EvalPrediction], Dict]`, `optional`):
             The function that will be used to compute metrics at evaluation. Must take a
             :class:`~transformers.EvalPrediction` and return a dictionary string to metric values.
-        tb_writer (:obj:`SummaryWriter`, `optional`):
-            Object to write to TensorBoard.
+        callbacks (List of :obj:`~transformers.TrainerCallback`, `optional`):
+            A list of callbacks to customize the training loop. Will add those to the list of default callbacks
+            detailed in :doc:`here <callback>`.
+
+            If you want to remove one of the default callbacks used, use the :meth:`Trainer.remove_callback` method.
         optimizers (:obj:`Tuple[torch.optim.Optimizer, torch.optim.lr_scheduler.LambdaLR`, `optional`):
             A tuple containing the optimizer and the scheduler to use. Will default to an instance of
             :class:`~transformers.AdamW` on your model and a scheduler given by
@@ -222,7 +186,7 @@ class Trainer:
 
     def __init__(
         self,
-        model: PreTrainedModel = None,
+        model: Union[PreTrainedModel, torch.nn.Module] = None,
         args: TrainingArguments = None,
         data_collator: Optional[DataCollator] = None,
         train_dataset: Optional[Dataset] = None,
@@ -230,7 +194,7 @@ class Trainer:
         tokenizer: Optional["PreTrainedTokenizerBase"] = None,
         model_init: Callable[[], PreTrainedModel] = None,
         compute_metrics: Optional[Callable[[EvalPrediction], Dict]] = None,
-        tb_writer: Optional["SummaryWriter"] = None,
+        callbacks: Optional[List[TrainerCallback]] = None,
         optimizers: Tuple[torch.optim.Optimizer, torch.optim.lr_scheduler.LambdaLR] = (None, None),
         **kwargs,
     ):
@@ -259,7 +223,21 @@ class Trainer:
                 "Passing a `model_init` is incompatible with providing the `optimizers` argument."
                 "You should subclass `Trainer` and override the `create_optimizer_and_scheduler` method."
             )
-        self.tb_writer = tb_writer
+        callbacks = DEFAULT_CALLBACKS if callbacks is None else DEFAULT_CALLBACKS + callbacks
+        self.callback_handler = CallbackHandler(callbacks, self.model, self.optimizer, self.lr_scheduler)
+        self.add_callback(PrinterCallback if self.args.disable_tqdm else ProgressCallback)
+
+        # Deprecated arguments
+        if "tb_writer" in kwargs:
+            warnings.warn(
+                "Passing `tb_writer` as a keyword argument is deprecated and won't be possible in a "
+                + "future version. Use `TensorBoardCallback(tb_writer=...)` instead and pass it to the `callbacks`"
+                + "argument",
+                FutureWarning,
+            )
+            tb_writer = kwargs.pop("tb_writer")
+            self.remove_callback(TensorBoardCallback)
+            self.add_callback(TensorBoardCallback(tb_writer=tb_writer))
         if "prediction_loss_only" in kwargs:
             warnings.warn(
                 "Passing `prediction_loss_only` as a keyword argument is deprecated and won't be possible in a "
@@ -270,13 +248,6 @@ class Trainer:
             self.args.prediction_loss_only = kwargs.pop("prediction_loss_only")
         assert kwargs == {}, f"Unexpected keyword arguments: {list(kwargs.keys())}."
 
-        if tb_writer is None and is_tensorboard_available() and self.is_world_process_zero():
-            self.tb_writer = SummaryWriter(log_dir=self.args.logging_dir)
-        if not is_tensorboard_available():
-            logger.warning(
-                "You are instantiating a Trainer but Tensorboard is not installed. You should consider installing it."
-            )
-
         # Will be set to True by `self._setup_loggers()` on first call to `self.log()`.
         self._loggers_initialized = False
 
@@ -304,6 +275,7 @@ class Trainer:
                 self._remove_unused_columns(self.eval_dataset, description="evaluation")
 
         self.state = TrainerState()
+        self.control = TrainerControl()
         # Internal variable for total_flos used to count as tensors (for distributed + TPU), will be sent in the
         # state at each call to self.log.
         self._total_flos = None
@@ -317,6 +289,45 @@ class Trainer:
             else ["labels"]
         )
         self.label_names = default_label_names if self.args.label_names is None else self.args.label_names
+        self.control = self.callback_handler.on_init_end(self.args, self.state, self.control)
+
+    def add_callback(self, callback):
+        """
+        Add a callback to the current list of :class:`~transformer.TrainerCallback`.
+
+        Args:
+           callback (:obj:`type` or :class:`~transformer.TrainerCallback`):
+               A :class:`~transformer.TrainerCallback` class or an instance of a :class:`~transformer.TrainerCallback`.
+               In the first case, will instantiate a member of that class.
+        """
+        self.callback_handler.add_callback(callback)
+
+    def pop_callback(self, callback):
+        """
+        Remove a callback from the current list of :class:`~transformer.TrainerCallback` and returns it.
+
+        If the callback is not found, returns :obj:`None` (and no error is raised).
+
+        Args:
+           callback (:obj:`type` or :class:`~transformer.TrainerCallback`):
+               A :class:`~transformer.TrainerCallback` class or an instance of a :class:`~transformer.TrainerCallback`.
+               In the first case, will pop the first member of that class found in the list of callbacks.
+
+        Returns:
+            :class:`~transformer.TrainerCallback`: The callback removed, if found.
+        """
+        return self.callback_handler.pop_callback(callback)
+
+    def remove_callback(self, callback):
+        """
+        Remove a callback from the current list of :class:`~transformer.TrainerCallback`.
+
+        Args:
+           callback (:obj:`type` or :class:`~transformer.TrainerCallback`):
+               A :class:`~transformer.TrainerCallback` class or an instance of a :class:`~transformer.TrainerCallback`.
+               In the first case, will remove the first member of that class found in the list of callbacks.
+        """
+        self.callback_handler.remove_callback(callback)
 
     def _remove_unused_columns(self, dataset: "datasets.Dataset", description: Optional[str] = None):
         if not self.args.remove_unused_columns:
@@ -465,102 +476,12 @@ class Trainer:
                 self.optimizer, num_warmup_steps=self.args.warmup_steps, num_training_steps=num_training_steps
             )
 
-    def setup_wandb(self):
-        """
-        Setup the optional Weights & Biases (`wandb`) integration.
-
-        One can subclass and override this method to customize the setup if needed. Find more information
-        `here <https://docs.wandb.com/huggingface>`__. You can also override the following environment variables:
-
-        Environment:
-            WANDB_WATCH:
-                (Optional, ["gradients", "all", "false"]) "gradients" by default, set to "false" to disable gradient logging
-                or "all" to log gradients and parameters
-            WANDB_PROJECT:
-                (Optional): str - "huggingface" by default, set this to a custom string to store results in a different project
-            WANDB_DISABLED:
-                (Optional): boolean - defaults to false, set to "true" to disable wandb entirely
-        """
-        if hasattr(self, "_setup_wandb"):
-            warnings.warn(
-                "The `_setup_wandb` method is deprecated and won't be called in a future version, define `setup_wandb` in your subclass.",
-                FutureWarning,
-            )
-            return self._setup_wandb()
-
-        if self.is_world_process_zero():
-            logger.info(
-                'Automatic Weights & Biases logging enabled, to disable set os.environ["WANDB_DISABLED"] = "true"'
-            )
-            combined_dict = {**self.args.to_sanitized_dict()}
-            if isinstance(self.model, PreTrainedModel):
-                combined_dict = {**self.model.config.to_dict(), **combined_dict}
-            wandb.init(
-                project=os.getenv("WANDB_PROJECT", "huggingface"), config=combined_dict, name=self.args.run_name
-            )
-            # keep track of model topology and gradients, unsupported on TPU
-            if not is_torch_tpu_available() and os.getenv("WANDB_WATCH") != "false":
-                wandb.watch(
-                    self.model, log=os.getenv("WANDB_WATCH", "gradients"), log_freq=max(100, self.args.logging_steps)
-                )
-
-    def setup_comet(self):
-        """
-        Setup the optional Comet.ml integration.
-
-        Environment:
-            COMET_MODE:
-                (Optional): str - "OFFLINE", "ONLINE", or "DISABLED"
-            COMET_PROJECT_NAME:
-                (Optional): str - Comet.ml project name for experiments
-            COMET_OFFLINE_DIRECTORY:
-                (Optional): str - folder to use for saving offline experiments when `COMET_MODE` is "OFFLINE"
-
-        For a number of configurable items in the environment,
-        see `here <https://www.comet.ml/docs/python-sdk/advanced/#comet-configuration-variables>`__
-        """
-        if self.is_world_master():
-            comet_mode = os.getenv("COMET_MODE", "ONLINE").upper()
-            args = {"project_name": os.getenv("COMET_PROJECT_NAME", "huggingface")}
-            experiment = None
-            if comet_mode == "ONLINE":
-                experiment = comet_ml.Experiment(**args)
-                logger.info("Automatic Comet.ml online logging enabled")
-            elif comet_mode == "OFFLINE":
-                args["offline_directory"] = os.getenv("COMET_OFFLINE_DIRECTORY", "./")
-                experiment = comet_ml.OfflineExperiment(**args)
-                logger.info("Automatic Comet.ml offline logging enabled; use `comet upload` when finished")
-            if experiment is not None:
-                experiment._set_model_graph(self.model, framework="transformers")
-                experiment._log_parameters(self.args, prefix="args/", framework="transformers")
-                if isinstance(self.model, PreTrainedModel):
-                    experiment._log_parameters(self.model.config, prefix="config/", framework="transformers")
-
     def num_examples(self, dataloader: DataLoader) -> int:
         """
         Helper to get number of samples in a :class:`~torch.utils.data.DataLoader` by accessing its dataset.
         """
         return len(dataloader.dataset)
 
-    def _setup_loggers(self):
-        if self._loggers_initialized:
-            return
-        if is_wandb_available():
-            self.setup_wandb()
-        elif os.environ.get("WANDB_DISABLED") != "true":
-            logger.info(
-                "You are instantiating a Trainer but W&B is not installed. To use wandb logging, "
-                "run `pip install wandb; wandb login` see https://docs.wandb.com/huggingface."
-            )
-        if is_comet_available():
-            self.setup_comet()
-        elif os.environ.get("COMET_MODE") != "DISABLED":
-            logger.info(
-                "To use comet_ml logging, run `pip/conda install comet_ml` "
-                "see https://www.comet.ml/docs/python-sdk/huggingface/"
-            )
-        self._loggers_initialized = True
-
     def _hp_search_setup(self, trial: Union["optuna.Trial", Dict[str, Any]]):
         """ HP search setup code """
         if self.hp_search_backend is None or trial is None:
@@ -661,7 +582,7 @@ class Trainer:
                 self.lr_scheduler.load_state_dict(torch.load(os.path.join(model_path, "scheduler.pt")))
             reissue_pt_warnings(caught_warnings)
 
-        # Moxed precision training with apex (torch < 1.6)
+        # Mixed precision training with apex (torch < 1.6)
         model = self.model
         if self.args.fp16 and _use_apex:
             if not is_apex_available():
@@ -687,10 +608,6 @@ class Trainer:
         # find_unused_parameters breaks checkpointing as per
         # https://github.com/huggingface/transformers/pull/4659#issuecomment-643356021
 
-        if self.tb_writer is not None:
-            self.tb_writer.add_text("args", self.args.to_json_string())
-            self.tb_writer.add_hparams(self.args.to_sanitized_dict(), metric_dict={})
-
         # Train!
         if is_torch_tpu_available():
             total_train_batch_size = self.args.train_batch_size * xm.xrt_world_size()
@@ -723,17 +640,25 @@ class Trainer:
             logger.info("  Continuing training from global step %d", self.state.global_step)
             logger.info("  Will skip the first %d steps in the first epoch", steps_trained_in_current_epoch)
 
+        # Update the references
+        self.callback_handler.model = self.model
+        self.callback_handler.optimizer = self.optimizer
+        self.callback_handler.lr_scheduler = self.lr_scheduler
+        self.callback_handler.train_dataloader = train_dataloader
         # This should be the same if the state has been saved but in case the training arguments changed, it's safer
         # to set this after the load.
         self.state.max_steps = max_steps
         self.state.num_train_epochs = num_train_epochs
+        self.state.is_local_process_zero = self.is_local_process_zero()
+        self.state.is_world_process_zero = self.is_world_process_zero()
 
         tr_loss = torch.tensor(0.0).to(self.args.device)
+        self._logging_loss_scalar = 0
         self._total_flos = self.state.total_flos
-        logging_loss_scalar = 0.0
         model.zero_grad()
-        disable_tqdm = self.args.disable_tqdm or not self.is_local_process_zero()
-        train_pbar = trange(epochs_trained, num_train_epochs, desc="Epoch", disable=disable_tqdm)
+
+        self.control = self.callback_handler.on_train_begin(self.args, self.state, self.control)
+
         for epoch in range(epochs_trained, num_train_epochs):
             if isinstance(train_dataloader, DataLoader) and isinstance(train_dataloader.sampler, DistributedSampler):
                 train_dataloader.sampler.set_epoch(epoch)
@@ -750,15 +675,18 @@ class Trainer:
             if self.args.past_index >= 0:
                 self._past = None
 
-            epoch_pbar = tqdm(epoch_iterator, desc="Iteration", disable=disable_tqdm)
+            self.control = self.callback_handler.on_epoch_begin(self.args, self.state, self.control)
+
             for step, inputs in enumerate(epoch_iterator):
 
                 # Skip past any already trained steps if resuming training
                 if steps_trained_in_current_epoch > 0:
                     steps_trained_in_current_epoch -= 1
-                    epoch_pbar.update(1)
                     continue
 
+                if (step + 1) % self.args.gradient_accumulation_steps == 0:
+                    self.control = self.callback_handler.on_step_begin(self.args, self.state, self.control)
+
                 tr_loss += self.training_step(model, inputs)
                 self._total_flos += self.floating_point_ops(inputs)
 
@@ -787,50 +715,15 @@ class Trainer:
                     model.zero_grad()
                     self.state.global_step += 1
                     self.state.epoch = epoch + (step + 1) / len(epoch_iterator)
+                    self.control = self.callback_handler.on_step_end(self.args, self.state, self.control)
+
+                    self._maybe_log_save_evalute(tr_loss, model, trial, epoch)
 
-                    if (self.args.logging_steps > 0 and self.state.global_step % self.args.logging_steps == 0) or (
-                        self.state.global_step == 1 and self.args.logging_first_step
-                    ):
-                        logs: Dict[str, float] = {}
-                        tr_loss_scalar = tr_loss.item()
-                        logs["loss"] = (tr_loss_scalar - logging_loss_scalar) / self.args.logging_steps
-                        # backward compatibility for pytorch schedulers
-                        logs["learning_rate"] = (
-                            self.lr_scheduler.get_last_lr()[0]
-                            if version.parse(torch.__version__) >= version.parse("1.4")
-                            else self.lr_scheduler.get_lr()[0]
-                        )
-                        logging_loss_scalar = tr_loss_scalar
-
-                        self.log(logs)
-
-                    if (
-                        self.args.evaluation_strategy == EvaluationStrategy.STEPS
-                        and self.state.global_step % self.args.eval_steps == 0
-                    ):
-                        metrics = self.evaluate()
-                        self._report_to_hp_search(trial, epoch, metrics)
-                        if self.args.load_best_model_at_end:
-                            self._save_training(model, trial, metrics=metrics)
-
-                    if (
-                        not self.args.load_best_model_at_end
-                        and self.args.save_steps > 0
-                        and self.state.global_step % self.args.save_steps == 0
-                    ):
-                        self._save_training(model, trial)
-
-                epoch_pbar.update(1)
-                if self.state.global_step >= max_steps:
+                if self.control.should_epoch_stop or self.control.should_training_stop:
                     break
-            epoch_pbar.close()
-            train_pbar.update(1)
 
-            if self.args.evaluation_strategy == EvaluationStrategy.EPOCH:
-                metrics = self.evaluate()
-                self._report_to_hp_search(trial, epoch, metrics)
-                if self.args.load_best_model_at_end:
-                    self._save_training(model, trial, metrics=metrics)
+            self.control = self.callback_handler.on_epoch_end(self.args, self.state, self.control)
+            self._maybe_log_save_evalute(tr_loss, model, trial, epoch)
 
             if self.args.tpu_metrics_debug or self.args.debug:
                 if is_torch_tpu_available():
@@ -841,12 +734,9 @@ class Trainer:
                         "You enabled PyTorch/XLA debug metrics but you don't have a TPU "
                         "configured. Check your training configuration if this is unexpected."
                     )
-            if self.state.global_step >= max_steps:
+            if self.control.should_training_stop:
                 break
 
-        train_pbar.close()
-        if self.tb_writer:
-            self.tb_writer.close()
         if self.args.past_index and hasattr(self, "_past"):
             # Clean the state at the end of training
             delattr(self, "_past")
@@ -863,9 +753,36 @@ class Trainer:
                 state_dict = torch.load(os.path.join(self.state.best_model_checkpoint, WEIGHTS_NAME))
                 self.model.load_state_dict(state_dict)
 
+        self.control = self.callback_handler.on_train_end(self.args, self.state, self.control)
+
         return TrainOutput(self.state.global_step, tr_loss.item() / self.state.global_step)
 
-    def _save_training(self, model, trial, metrics=None):
+    def _maybe_log_save_evalute(self, tr_loss, model, trial, epoch):
+        if self.control.should_log:
+            logs: Dict[str, float] = {}
+            tr_loss_scalar = tr_loss.item()
+            logs["loss"] = (tr_loss_scalar - self._logging_loss_scalar) / self.args.logging_steps
+            # backward compatibility for pytorch schedulers
+            logs["learning_rate"] = (
+                self.lr_scheduler.get_last_lr()[0]
+                if version.parse(torch.__version__) >= version.parse("1.4")
+                else self.lr_scheduler.get_lr()[0]
+            )
+            self._logging_loss_scalar = tr_loss_scalar
+
+            self.log(logs)
+
+        metrics = None
+        if self.control.should_evaluate:
+            metrics = self.evaluate()
+            self._report_to_hp_search(trial, epoch, metrics)
+            self.control = self.callback_handler.on_evaluate(self.args, self.state, self.control, metrics)
+
+        if self.control.should_save:
+            self._save_checkpoint(model, trial, metrics=metrics)
+            self.control = self.callback_handler.on_save(self.args, self.state, self.control)
+
+    def _save_checkpoint(self, model, trial, metrics=None):
         # In all cases (even distributed/parallel), self.model is always a reference
         # to the model we want to save.
         if hasattr(model, "module"):
@@ -896,7 +813,7 @@ class Trainer:
             reissue_pt_warnings(caught_warnings)
 
         # Determine the new best metric / best model checkpoint
-        if metrics is not None:
+        if metrics is not None and self.args.metric_for_best_model is not None:
             metric_to_check = self.args.metric_for_best_model
             if not metric_to_check.startswith("eval_"):
                 metric_to_check = f"eval_{metric_to_check}"
@@ -998,7 +915,7 @@ class Trainer:
         self.hp_search_backend = None
         return best_run
 
-    def log(self, logs: Dict[str, float], iterator: Optional[tqdm] = None) -> None:
+    def log(self, logs: Dict[str, float]) -> None:
         """
         Log :obj:`logs` on the various objects watching training.
 
@@ -1007,55 +924,22 @@ class Trainer:
         Args:
             logs (:obj:`Dict[str, float]`):
                 The values to log.
-            iterator (:obj:`tqdm`, `optional`):
-                A potential tqdm progress bar to write the logs on.
         """
-        # Set up loggers like W&B or Comet ML
-        self._setup_loggers()
-
         if hasattr(self, "_log"):
             warnings.warn(
                 "The `_log` method is deprecated and won't be called in a future version, define `log` in your subclass.",
                 FutureWarning,
             )
-            return self._log(logs, iterator=iterator)
+            return self._log(logs)
 
         if self.state.epoch is not None:
             logs["epoch"] = self.state.epoch
         if self._total_flos is not None:
             self.store_flos()
             logs["total_flos"] = self.state.total_flos
-        if self.tb_writer:
-            for k, v in logs.items():
-                if isinstance(v, (int, float)):
-                    self.tb_writer.add_scalar(k, v, self.state.global_step)
-                else:
-                    logger.warning(
-                        "Trainer is attempting to log a value of "
-                        '"%s" of type %s for key "%s" as a scalar. '
-                        "This invocation of Tensorboard's writer.add_scalar() "
-                        "is incorrect so we dropped this attribute.",
-                        v,
-                        type(v),
-                        k,
-                    )
-            self.tb_writer.flush()
-        if is_wandb_available():
-            if self.is_world_process_zero():
-                wandb.log(logs, step=self.state.global_step)
-        if is_comet_available():
-            if self.is_world_process_zero():
-                experiment = comet_ml.config.get_global_experiment()
-                if experiment is not None:
-                    experiment._log_metrics(
-                        logs, step=self.state.global_step, epoch=self.state.epoch, framework="transformers"
-                    )
+        self.control = self.callback_handler.on_log(self.args, self.state, self.control, logs)
         output = {**logs, **{"step": self.state.global_step}}
         self.state.log_history.append(output)
-        if iterator is not None:
-            iterator.write(output)
-        else:
-            print(output)
 
     def _prepare_inputs(self, inputs: Dict[str, Union[torch.Tensor, Any]]) -> Dict[str, Union[torch.Tensor, Any]]:
         """
@@ -1372,8 +1256,9 @@ class Trainer:
         if self.args.past_index >= 0:
             self._past = None
 
-        disable_tqdm = not self.is_local_process_zero() or self.args.disable_tqdm
-        for inputs in tqdm(dataloader, desc=description, disable=disable_tqdm):
+        self.callback_handler.eval_dataloader = dataloader
+
+        for inputs in dataloader:
             loss, logits, labels = self.prediction_step(model, inputs, prediction_loss_only)
             batch_size = inputs[list(inputs.keys())[0]].shape[0]
             if loss is not None:
@@ -1382,6 +1267,7 @@ class Trainer:
                 preds = logits if preds is None else nested_concat(preds, logits, dim=0)
             if labels is not None:
                 label_ids = labels if label_ids is None else nested_concat(label_ids, labels, dim=0)
+            self.control = self.callback_handler.on_prediction_step(self.args, self.state, self.control)
 
         if self.args.past_index and hasattr(self, "_past"):
             # Clean the state at the end of the evaluation loop

src/transformers/trainer_callback.py

+# coding=utf-8
+# Copyright 2020-present the HuggingFace Inc. team.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+"""
+Callbacks to use with the Trainer class and customize the training loop.
+"""
+
+import dataclasses
+import json
+from dataclasses import dataclass
+from typing import Dict, List, Optional
+
+from tqdm.auto import tqdm
+
+from .trainer_utils import EvaluationStrategy
+from .training_args import TrainingArguments
+from .utils import logging
+
+
+logger = logging.get_logger(__name__)
+
+
+@dataclass
+class TrainerState:
+    """
+    A class containing the :class:`~transformers.Trainer` inner state that will be saved along the model and optimizer
+    when checkpointing and passed to the :class:`~transformers.TrainerCallback`.
+
+    .. note::
+
+        In all this class, one step is to be understood as one update step. When using gradient accumulation, one
+        update step may require several forward and backward passes: if you use :obj:`gradient_accumulation_steps=n`,
+        then one update step requires going throuch `n` batches.
+
+    Args:
+        epoch (:obj:`float`, `optional`):
+            Only set during training, will represent the epoch the training is at (the decimal part being the
+            percentage of the current epoch completed).
+        global_step (:obj:`int`, `optional`, defaults to 0):
+            During training, represents the number of update steps completed.
+        max_steps (:obj:`int`, `optional`, defaults to 0):
+            The number of update steps to do during the current training.
+        total_flos (:obj:`int`, `optional`, defaults to 0):
+            The total number of floating operations done by the model since the beginning of training.
+        log_history (:obj:`List[Dict[str, float]]`, `optional`):
+            The list of logs done since the beginning of training.
+        best_metric (:obj:`float`, `optional`):
+            When tracking the best model, the value of the best metric encountered so far.
+        best_model_checkpoint (:obj:`str`, `optional`):
+            When tracking the best model, the value of the name of the checkpoint for the best model encountered so
+            far.
+        is_local_process_zero (:obj:`bool`, `optional`, defaults to :obj:`True`):
+            Whether or not this process is the local (e.g., on one machine if training in a distributed fashion on
+            several machines) main process.
+        is_world_process_zero (:obj:`bool`, `optional`, defaults to :obj:`True`):
+            Whether or not this process is the global main process (when training in a distributed fashion on
+            several machines, this is only going to be :obj:`True` for one process).
+    """
+
+    epoch: Optional[float] = None
+    global_step: int = 0
+    max_steps: int = 0
+    num_train_epochs: int = 0
+    total_flos: int = 0
+    log_history: List[Dict[str, float]] = None
+    best_metric: Optional[float] = None
+    best_model_checkpoint: Optional[str] = None
+    is_local_process_zero: bool = True
+    is_world_process_zero: bool = True
+
+    def __post_init__(self):
+        if self.log_history is None:
+            self.log_history = []
+
+    def save_to_json(self, json_path: str):
+        """ Save the content of this instance in JSON format inside :obj:`json_path`."""
+        json_string = json.dumps(dataclasses.asdict(self), indent=2, sort_keys=True) + "\n"
+        with open(json_path, "w", encoding="utf-8") as f:
+            f.write(json_string)
+
+    @classmethod
+    def load_from_json(cls, json_path: str):
+        """ Create an instance from the content of :obj:`json_path`."""
+        with open(json_path, "r", encoding="utf-8") as f:
+            text = f.read()
+        return cls(**json.loads(text))
+
+
+@dataclass
+class TrainerControl:
+    """
+    A class that handles the :class:`~transformers.Trainer` control flow. This class is used by the
+    :class:`~transformers.TrainerCallback` to activate some switches in the training loop.
+
+    Args:
+        should_training_stop (:obj:`bool`, `optional`, defaults to :obj:`False`):
+            Whether or not the training should be interrupted.
+
+            If :obj:`True`, this variable will not be set back to :obj:`False`. The training will just stop.
+        should_epoch_stop (:obj:`bool`, `optional`, defaults to :obj:`False`):
+            Whether or not the current epoch should be interrupted.
+
+            If :obj:`True`, this variable will be set back to :obj:`False` at the beginning of the next epoch.
+        should_save (:obj:`bool`, `optional`, defaults to :obj:`False`):
+            Whether or not the model should be saved at this step.
+
+            If :obj:`True`, this variable will be set back to :obj:`False` at the beginning of the next step.
+        should_evaluate (:obj:`bool`, `optional`, defaults to :obj:`False`):
+            Whether or not the model should be evaluated at this step.
+
+            If :obj:`True`, this variable will be set back to :obj:`False` at the beginning of the next step.
+        should_log (:obj:`bool`, `optional`, defaults to :obj:`False`):
+            Whether or not the logs should be reported at this step.
+
+            If :obj:`True`, this variable will be set back to :obj:`False` at the beginning of the next step.
+    """
+
+    should_training_stop: bool = False
+    should_epoch_stop: bool = False
+    should_save: bool = False
+    should_evaluate: bool = False
+    should_log: bool = False
+
+    def _new_training(self):
+        """ Internal method that resets the variable for a new training. """
+        self.should_training_stop = False
+
+    def _new_epoch(self):
+        """ Internal method that resets the variable for a new epoch. """
+        self.should_epoch_stop = False
+
+    def _new_step(self):
+        """ Internal method that resets the variable for a new step. """
+        self.should_save_model = False
+        self.should_evaluate = False
+        self.should_log = False
+
+
+class TrainerCallback:
+    """
+    A class for objects that will inspect the state of the training loop at some events and take some decisions. At
+    each of those events the following arguments are available:
+
+    Args:
+        args (:class:`~transformers.TrainingArguments`):
+            The training arguments used to instantiate the :class:`~transformers.Trainer`.
+        state (:class:`~transformers.TrainerState`):
+            The current state of the :class:`~transformers.Trainer`.
+        control (:class:`~transformers.TrainerControl`):
+            The object that is returned to the :class:`~transformers.Trainer` and can be used to make some decisions.
+        model (:class:`~transformers.PreTrainedModel` or :obj:`torch.nn.Module`):
+            The model being trained.
+        optimizer (:obj:`torch.optim.Optimizer`):
+            The optimizer used for the training steps.
+        lr_scheduler (:obj:`torch.optim.lr_scheduler.LambdaLR`):
+            The scheduler used for setting the learning rate.
+        train_dataloader (:obj:`torch.utils.data.dataloader.DataLoader`, `optional`):
+            The current dataloader used for training.
+        eval_dataloader (:obj:`torch.utils.data.dataloader.DataLoader`, `optional`):
+            The current dataloader used for training.
+        metrics (:obj:`Dict[str, float]`):
+            The metrics computed by the last evaluation phase.
+
+            Those are only accessible in the event :obj:`on_evaluate`.
+        logs  (:obj:`Dict[str, float]`):
+            The values to log.
+
+            Those are only accessible in the event :obj:`on_log`.
+
+    The :obj:`control` object is the only one that can be changed by the callback, in which case the event that changes
+    it should return the modified version.
+
+    The argument :obj:`args`, :obj:`state` and :obj:`control` are positionals for all events, all the others are
+    grouped in :obj:`kwargs`. You can unpack the ones you need in the signature of the event using them. As an example,
+    see the code of the simple :class:`~transformer.PrinterCallback`.
+
+    Example::
+
+        class PrinterCallback(TrainerCallback):
+
+            def on_log(self, args, state, control, logs=None, **kwargs):
+                _ = logs.pop("total_flos", None)
+                if state.is_local_process_zero:
+                    print(logs)
+    """
+
+    def on_init_end(self, args: TrainingArguments, state: TrainerState, control: TrainerControl, **kwargs):
+        """
+        Event called at the end of the initialization of the :class:`~transformers.Trainer`.
+        """
+        pass
+
+    def on_train_begin(self, args: TrainingArguments, state: TrainerState, control: TrainerControl, **kwargs):
+        """
+        Event called at the beginning of training.
+        """
+        pass
+
+    def on_train_end(self, args: TrainingArguments, state: TrainerState, control: TrainerControl, **kwargs):
+        """
+        Event called at the end of training.
+        """
+        pass
+
+    def on_epoch_begin(self, args: TrainingArguments, state: TrainerState, control: TrainerControl, **kwargs):
+        """
+        Event called at the beginning of an epoch.
+        """
+        pass
+
+    def on_epoch_end(self, args: TrainingArguments, state: TrainerState, control: TrainerControl, **kwargs):
+        """
+        Event called at the end of an epoch.
+        """
+        pass
+
+    def on_step_begin(self, args: TrainingArguments, state: TrainerState, control: TrainerControl, **kwargs):
+        """
+        Event called at the beginning of a training step. If using gradient accumulation, one training step might take
+        several inputs.
+        """
+        pass
+
+    def on_step_end(self, args: TrainingArguments, state: TrainerState, control: TrainerControl, **kwargs):
+        """
+        Event called at the end of a training step. If using gradient accumulation, one training step might take
+        several inputs.
+        """
+        pass
+
+    def on_evaluate(self, args: TrainingArguments, state: TrainerState, control: TrainerControl, **kwargs):
+        """
+        Event called after an evaluation phase.
+        """
+        pass
+
+    def on_save(self, args: TrainingArguments, state: TrainerState, control: TrainerControl, **kwargs):
+        """
+        Event called after a checkpoint save.
+        """
+        pass
+
+    def on_log(self, args: TrainingArguments, state: TrainerState, control: TrainerControl, **kwargs):
+        """
+        Event called after logging the last logs.
+        """
+        pass
+
+    def on_prediction_step(self, args: TrainingArguments, state: TrainerState, control: TrainerControl, **kwargs):
+        """
+        Event called after a prediction step.
+        """
+        pass
+
+
+class CallbackHandler(TrainerCallback):
+    """ Internal class that just calls the list of callbacks in order. """
+
+    def __init__(self, callbacks, model, optimizer, lr_scheduler):
+        self.callbacks = []
+        for cb in callbacks:
+            self.add_callback(cb)
+        self.model = model
+        self.optimizer = optimizer
+        self.lr_scheduler = lr_scheduler
+        self.train_dataloader = None
+        self.eval_dataloader = None
+
+        if not any(isinstance(cb, DefaultFlowCallback) for cb in self.callbacks):
+            logger.warn(
+                "The Trainer will not work properly if you don't have a `DefaultFlowCallback` in its callbacks. You\n"
+                + "should add one before training with `trainer.add_callback(DefaultFlowCallback). The current list of"
+                + "callbacks is\n:"
+                + self.callback_list
+            )
+
+    def add_callback(self, callback):
+        cb = callback() if isinstance(callback, type) else callback
+        cb_class = callback if isinstance(callback, type) else callback.__class__
+        if cb_class in [c.__class__ for c in self.callbacks]:
+            logger.warn(
+                f"You are adding a {cb_class} to the callbacks of this Trainer, but there is already one. The current"
+                + "list of callbacks is\n:"
+                + self.callback_list
+            )
+        self.callbacks.append(cb)
+
+    def pop_callback(self, callback):
+        if isinstance(callback, type):
+            for cb in self.callbacks:
+                if isinstance(cb, callback):
+                    self.callbacks.remove(cb)
+                    return cb
+        else:
+            for cb in self.callbacks:
+                if cb == callback:
+                    self.callbacks.remove(cb)
+                    return cb
+
+    def remove_callback(self, callback):
+        if isinstance(callback, type):
+            for cb in self.callbacks:
+                if isinstance(cb, callback):
+                    self.callbacks.remove(cb)
+                    return
+        else:
+            self.callbacks.remove(callback)
+
+    @property
+    def callback_list(self):
+        return "\n".join(self.callbacks)
+
+    def on_init_end(self, args: TrainingArguments, state: TrainerState, control: TrainerControl):
+        return self.call_event("on_init_end", args, state, control)
+
+    def on_train_begin(self, args: TrainingArguments, state: TrainerState, control: TrainerControl):
+        control.should_training_stop = False
+        return self.call_event("on_train_begin", args, state, control)
+
+    def on_train_end(self, args: TrainingArguments, state: TrainerState, control: TrainerControl):
+        return self.call_event("on_train_end", args, state, control)
+
+    def on_epoch_begin(self, args: TrainingArguments, state: TrainerState, control: TrainerControl):
+        control.should_epoch_stop = False
+        return self.call_event("on_epoch_begin", args, state, control)
+
+    def on_epoch_end(self, args: TrainingArguments, state: TrainerState, control: TrainerControl):
+        return self.call_event("on_epoch_end", args, state, control)
+
+    def on_step_begin(self, args: TrainingArguments, state: TrainerState, control: TrainerControl):
+        control.should_log = False
+        control.should_evaluate = False
+        control.should_save = False
+        return self.call_event("on_step_begin", args, state, control)
+
+    def on_step_end(self, args: TrainingArguments, state: TrainerState, control: TrainerControl):
+        return self.call_event("on_step_end", args, state, control)
+
+    def on_evaluate(self, args: TrainingArguments, state: TrainerState, control: TrainerControl, metrics):
+        control.should_evaluate = False
+        return self.call_event("on_evaluate", args, state, control, metrics=metrics)
+
+    def on_save(self, args: TrainingArguments, state: TrainerState, control: TrainerControl):
+        control.should_save = False
+        return self.call_event("on_save", args, state, control)
+
+    def on_log(self, args: TrainingArguments, state: TrainerState, control: TrainerControl, logs):
+        control.should_log = False
+        return self.call_event("on_log", args, state, control, logs=logs)
+
+    def on_prediction_step(self, args: TrainingArguments, state: TrainerState, control: TrainerControl):
+        return self.call_event("on_prediction_step", args, state, control)
+
+    def call_event(self, event, args, state, control, **kwargs):
+        for callback in self.callbacks:
+            result = getattr(callback, event)(
+                args,
+                state,
+                control,
+                model=self.model,
+                optimizer=self.optimizer,
+                lr_scheduler=self.lr_scheduler,
+                train_dataloader=self.train_dataloader,
+                eval_dataloader=self.eval_dataloader,
+                **kwargs,
+            )
+            # A Callback can skip the return of `control` if it doesn't change it.
+            if result is not None:
+                control = result
+        return control
+
+
+class DefaultFlowCallback(TrainerCallback):
+    """
+    A :class:`~transformers.TrainerCallback` that handles the default flow of the training loop for logs, evaluation
+    and checkpoints.
+    """
+
+    def on_step_end(self, args: TrainingArguments, state: TrainerState, control: TrainerControl, **kwargs):
+        # Log
+        if state.global_step == 1 and args.logging_first_step:
+            control.should_log = True
+        if args.logging_steps > 0 and state.global_step % args.logging_steps == 0:
+            control.should_log = True
+
+        # Evaluate
+        if args.evaluation_strategy == EvaluationStrategy.STEPS and state.global_step % args.eval_steps == 0:
+            control.should_evaluate = True
+            if args.load_best_model_at_end:
+                control.should_save = True
+
+        # Save
+        if not args.load_best_model_at_end and args.save_steps > 0 and state.global_step % args.save_steps == 0:
+            control.should_save = True
+
+        # End training
+        if state.global_step >= state.max_steps:
+            control.should_training_stop = True
+
+        return control
+
+    def on_epoch_end(self, args: TrainingArguments, state: TrainerState, control: TrainerControl, **kwargs):
+        if args.evaluation_strategy == EvaluationStrategy.EPOCH:
+            control.should_evaluate = True
+            if args.load_best_model_at_end:
+                control.should_save = True
+        return control
+
+
+class ProgressCallback(TrainerCallback):
+    """
+    A :class:`~transformers.TrainerCallback` that displays the progress of training or evaluation.
+    """
+
+    def __init__(self):
+        self.training_bar = None
+        self.prediction_bar = None
+
+    def on_train_begin(self, args, state, control, **kwargs):
+        if state.is_local_process_zero:
+            self.training_bar = tqdm(total=state.max_steps)
+
+    def on_step_end(self, args, state, control, **kwargs):
+        if state.is_local_process_zero:
+            self.training_bar.update(1)
+
+    def on_prediction_step(self, args, state, control, eval_dataloader=None, **kwargs):
+        if state.is_local_process_zero:
+            if self.prediction_bar is None:
+                self.prediction_bar = tqdm(total=len(eval_dataloader), leave=self.training_bar is None)
+            self.prediction_bar.update(1)
+
+    def on_evaluate(self, args, state, control, **kwargs):
+        if state.is_local_process_zero:
+            self.prediction_bar.close()
+            self.prediction_bar = None
+
+    def on_log(self, args, state, control, logs=None, **kwargs):
+        if state.is_local_process_zero and self.training_bar is not None:
+            _ = logs.pop("total_flos", None)
+            self.training_bar.write(str(logs))
+
+    def on_train_end(self, args, state, control, **kwargs):
+        if state.is_local_process_zero:
+            self.training_bar.close()
+            self.training_bar = None
+
+
+class PrinterCallback(TrainerCallback):
+    """
+    A bare :class:`~transformers.TrainerCallback` that just prints the logs.
+    """
+
+    def on_log(self, args, state, control, logs=None, **kwargs):
+        _ = logs.pop("total_flos", None)
+        if state.is_local_process_zero:
+            print(logs)

src/transformers/trainer_pt_utils.py

+# coding=utf-8
+# Copyright 2020-present the HuggingFace Inc. team.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+"""
+Torch utilities for the Trainer class.
+"""
+
+import math
+import warnings
+from contextlib import contextmanager
+from typing import List, Optional, Union
+
+import torch
+from torch.utils.data.distributed import DistributedSampler
+from torch.utils.data.sampler import RandomSampler, Sampler
+
+from .file_utils import is_torch_tpu_available
+
+
+if is_torch_tpu_available():
+    import torch_xla.core.xla_model as xm
+
+PT_LR_SCHEDULER_WARNING = "Please also save or load the state of the optimzer when saving or loading the scheduler."
+
+
+def nested_concat(tensors, new_tensors, dim=0):
+    "Concat the `new_tensors` to `tensors` on `dim`. Works for tensors or nested list/tuples of tensors."
+    assert type(tensors) == type(
+        new_tensors
+    ), f"Expected `tensors` and `new_tensors` to have the same type but found {type(tensors)} and {type(new_tensors)}."
+    if isinstance(tensors, (list, tuple)):
+        return type(tensors)(nested_concat(t, n, dim) for t, n in zip(tensors, new_tensors))
+    return torch.cat((tensors, new_tensors), dim=dim)
+
+
+def nested_numpify(tensors):
+    "Numpify `tensors` (even if it's a nested list/tuple of tensors)."
+    if isinstance(tensors, (list, tuple)):
+        return type(tensors)(nested_numpify(t) for t in tensors)
+    return tensors.cpu().numpy()
+
+
+def nested_detach(tensors):
+    "Detach `tensors` (even if it's a nested list/tuple of tensors)."
+    if isinstance(tensors, (list, tuple)):
+        return type(tensors)(nested_detach(t) for t in tensors)
+    return tensors.detach()
+
+
+def nested_xla_mesh_reduce(tensors, name):
+    if is_torch_tpu_available():
+        import torch_xla.core.xla_model as xm
+
+        if isinstance(tensors, (list, tuple)):
+            return type(tensors)(nested_xla_mesh_reduce(t, f"{name}_{i}") for i, t in enumerate(tensors))
+        return xm.mesh_reduce(name, tensors, torch.cat)
+    else:
+        raise ImportError("Torch xla must be installed to use `nested_xla_mesh_reduce`")
+
+
+def distributed_concat(tensor: "torch.Tensor", num_total_examples: Optional[int] = None) -> torch.Tensor:
+    try:
+        if isinstance(tensor, (tuple, list)):
+            return type(tensor)(distributed_concat(t, num_total_examples) for t in tensor)
+        output_tensors = [tensor.clone() for _ in range(torch.distributed.get_world_size())]
+        torch.distributed.all_gather(output_tensors, tensor)
+        concat = torch.cat(output_tensors, dim=0)
+
+        # truncate the dummy elements added by SequentialDistributedSampler
+        if num_total_examples is not None:
+            concat = concat[:num_total_examples]
+        return concat
+    except AssertionError:
+        raise AssertionError("Not currently using distributed training")
+
+
+def distributed_broadcast_scalars(
+    scalars: List[Union[int, float]], num_total_examples: Optional[int] = None
+) -> torch.Tensor:
+    try:
+        tensorized_scalar = torch.tensor(scalars).cuda()
+        output_tensors = [tensorized_scalar.clone() for _ in range(torch.distributed.get_world_size())]
+        torch.distributed.all_gather(output_tensors, tensorized_scalar)
+        concat = torch.cat(output_tensors, dim=0)
+
+        # truncate the dummy elements added by SequentialDistributedSampler
+        if num_total_examples is not None:
+            concat = concat[:num_total_examples]
+        return concat
+    except AssertionError:
+        raise AssertionError("Not currently using distributed training")
+
+
+def reissue_pt_warnings(caught_warnings):
+    # Reissue warnings that are not the PT_LR_SCHEDULER_WARNING
+    if len(caught_warnings) > 1:
+        for w in caught_warnings:
+            if w.category != UserWarning or w.message != PT_LR_SCHEDULER_WARNING:
+                warnings.warn(w.message, w.category)
+
+
+@contextmanager
+def torch_distributed_zero_first(local_rank: int):
+    """
+    Decorator to make all processes in distributed training wait for each local_master to do something.
+
+    Args:
+        local_rank (:obj:`int`): The rank of the local process.
+    """
+    if local_rank not in [-1, 0]:
+        torch.distributed.barrier()
+    yield
+    if local_rank == 0:
+        torch.distributed.barrier()
+
+
+class SequentialDistributedSampler(Sampler):
+    """
+    Distributed Sampler that subsamples indicies sequentially,
+    making it easier to collate all results at the end.
+
+    Even though we only use this sampler for eval and predict (no training),
+    which means that the model params won't have to be synced (i.e. will not hang
+    for synchronization even if varied number of forward passes), we still add extra
+    samples to the sampler to make it evenly divisible (like in `DistributedSampler`)
+    to make it easy to `gather` or `reduce` resulting tensors at the end of the loop.
+    """
+
+    def __init__(self, dataset, num_replicas=None, rank=None):
+        if num_replicas is None:
+            if not torch.distributed.is_available():
+                raise RuntimeError("Requires distributed package to be available")
+            num_replicas = torch.distributed.get_world_size()
+        if rank is None:
+            if not torch.distributed.is_available():
+                raise RuntimeError("Requires distributed package to be available")
+            rank = torch.distributed.get_rank()
+        self.dataset = dataset
+        self.num_replicas = num_replicas
+        self.rank = rank
+        self.num_samples = int(math.ceil(len(self.dataset) * 1.0 / self.num_replicas))
+        self.total_size = self.num_samples * self.num_replicas
+
+    def __iter__(self):
+        indices = list(range(len(self.dataset)))
+
+        # add extra samples to make it evenly divisible
+        indices += indices[: (self.total_size - len(indices))]
+        assert (
+            len(indices) == self.total_size
+        ), f"Indices length {len(indices)} and total size {self.total_size} mismatched"
+
+        # subsample
+        indices = indices[self.rank * self.num_samples : (self.rank + 1) * self.num_samples]
+        assert (
+            len(indices) == self.num_samples
+        ), f"Indices length {len(indices)} and sample number {self.num_samples} mismatched"
+
+        return iter(indices)
+
+    def __len__(self):
+        return self.num_samples
+
+
+def get_tpu_sampler(dataset: torch.utils.data.dataset.Dataset):
+    if xm.xrt_world_size() <= 1:
+        return RandomSampler(dataset)
+    return DistributedSampler(dataset, num_replicas=xm.xrt_world_size(), rank=xm.get_ordinal())

src/transformers/trainer_utils.py

-import dataclasses
-import json
+# coding=utf-8
+# Copyright 2020-present the HuggingFace Inc. team.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+"""
+Utilities for the Trainer and TFTrainer class. Should be independent from PyTorch and TensorFlow.
+"""
+
 import random
-from dataclasses import dataclass
-from typing import Any, Dict, List, NamedTuple, Optional, Tuple, Union
+from typing import Any, Dict, NamedTuple, Optional, Tuple, Union
 
 import numpy as np
 
-from .file_utils import is_tf_available, is_torch_available, is_torch_tpu_available
+from .file_utils import is_tf_available, is_torch_available
 from .tokenization_utils_base import ExplicitEnum
 
 
-if is_torch_available():
-    import torch
-
-
 def set_seed(seed: int):
     """
     Helper function for reproducible behavior to set the seed in ``random``, ``numpy``, ``torch`` and/or ``tf``
@@ -139,144 +150,3 @@ default_hp_space = {
     HPSearchBackend.OPTUNA: default_hp_space_optuna,
     HPSearchBackend.RAY: default_hp_space_ray,
 }
-
-
-def nested_concat(tensors, new_tensors, dim=0):
-    "Concat the `new_tensors` to `tensors` on `dim`. Works for tensors or nested list/tuples of tensors."
-    if is_torch_available():
-        assert type(tensors) == type(
-            new_tensors
-        ), f"Expected `tensors` and `new_tensors` to have the same type but found {type(tensors)} and {type(new_tensors)}."
-        if isinstance(tensors, (list, tuple)):
-            return type(tensors)(nested_concat(t, n, dim) for t, n in zip(tensors, new_tensors))
-        return torch.cat((tensors, new_tensors), dim=dim)
-    else:
-        raise ImportError("Torch must be installed to use `nested_concat`")
-
-
-def nested_deatch(tensors):
-    "Detach `tensors` (even if it's a nested list/tuple of tensors)."
-    if isinstance(tensors, (list, tuple)):
-        return type(tensors)(nested_detach(t) for t in tensors)
-    return tensors.detach()
-
-
-def nested_numpify(tensors):
-    "Numpify `tensors` (even if it's a nested list/tuple of tensors)."
-    if isinstance(tensors, (list, tuple)):
-        return type(tensors)(nested_numpify(t) for t in tensors)
-    return tensors.cpu().numpy()
-
-
-def nested_detach(tensors):
-    "Detach `tensors` (even if it's a nested list/tuple of tensors)."
-    if isinstance(tensors, (list, tuple)):
-        return type(tensors)(nested_detach(t) for t in tensors)
-    return tensors.detach()
-
-
-def nested_xla_mesh_reduce(tensors, name):
-    if is_torch_tpu_available():
-        import torch_xla.core.xla_model as xm
-
-        if isinstance(tensors, (list, tuple)):
-            return type(tensors)(nested_xla_mesh_reduce(t, f"{name}_{i}") for i, t in enumerate(tensors))
-        return xm.mesh_reduce(name, tensors, torch.cat)
-    else:
-        raise ImportError("Torch xla must be installed to use `nested_xla_mesh_reduce`")
-
-
-def distributed_concat(tensor: "torch.Tensor", num_total_examples: Optional[int] = None) -> "torch.Tensor":
-    if is_torch_available():
-        try:
-            if isinstance(tensor, (tuple, list)):
-                return type(tensor)(distributed_concat(t, num_total_examples) for t in tensor)
-            output_tensors = [tensor.clone() for _ in range(torch.distributed.get_world_size())]
-            torch.distributed.all_gather(output_tensors, tensor)
-            concat = torch.cat(output_tensors, dim=0)
-
-            # truncate the dummy elements added by SequentialDistributedSampler
-            if num_total_examples is not None:
-                concat = concat[:num_total_examples]
-            return concat
-        except AssertionError:
-            raise AssertionError("Not currently using distributed training")
-    else:
-        raise ImportError("Torch must be installed to use `distributed_concat`")
-
-
-def distributed_broadcast_scalars(
-    scalars: List[Union[int, float]], num_total_examples: Optional[int] = None
-) -> "torch.Tensor":
-    if is_torch_available():
-        try:
-            tensorized_scalar = torch.tensor(scalars).cuda()
-            output_tensors = [tensorized_scalar.clone() for _ in range(torch.distributed.get_world_size())]
-            torch.distributed.all_gather(output_tensors, tensorized_scalar)
-            concat = torch.cat(output_tensors, dim=0)
-
-            # truncate the dummy elements added by SequentialDistributedSampler
-            if num_total_examples is not None:
-                concat = concat[:num_total_examples]
-            return concat
-        except AssertionError:
-            raise AssertionError("Not currently using distributed training")
-    else:
-        raise ImportError("Torch must be installed to use `distributed_broadcast_scalars`")
-
-
-@dataclass
-class TrainerState:
-    """
-    A class containing the `Trainer` inner state that will be saved along the model and optimizer.
-
-    .. note::
-
-        In all this class, one step is to be understood as one update step. When using gradient accumulation, one
-        update step may require several forward and backward passes: if you use :obj:`gradient_accumulation_steps=n`,
-        then one update step requires going throuch `n` batches.
-
-    Args:
-        epoch (:obj:`float`, `optional`):
-            Only set during training, will represent the epoch the training is at (the decimal part being the
-            percentage of the current epoch completed).
-        global_step (:obj:`int`, `optional`, defaults to 0):
-            During training, represents the number of update steps completed.
-        max_steps (:obj:`int`, `optional`, defaults to 0):
-            The number of update steps to do during the current training.
-        total_flos (:obj:`int`, `optional`, defaults to 0):
-            The total number of floating operations done by the model since the beginning of training.
-        log_history (:obj:`List[Dict[str, float]]`, `optional`):
-            The list of logs done since the beginning of training.
-        best_metric (:obj:`float`, `optional`):
-            When tracking the best model, the value of the best metric encountered so far.
-        best_model_checkpoint (:obj:`str`, `optional`):
-            When tracking the best model, the value of the name of the checkpoint for the best model encountered so
-            far.
-    """
-
-    epoch: Optional[float] = None
-    global_step: int = 0
-    max_steps: int = 0
-    num_train_epochs: int = 0
-    total_flos: int = 0
-    log_history: List[Dict[str, float]] = None
-    best_metric: Optional[float] = None
-    best_model_checkpoint: Optional[str] = None
-
-    def __post_init__(self):
-        if self.log_history is None:
-            self.log_history = []
-
-    def save_to_json(self, json_path: str):
-        """ Save the content of this instance in JSON format inside :obj:`json_path`."""
-        json_string = json.dumps(dataclasses.asdict(self), indent=2, sort_keys=True) + "\n"
-        with open(json_path, "w", encoding="utf-8") as f:
-            f.write(json_string)
-
-    @classmethod
-    def load_from_json(cls, json_path: str):
-        """ Create an instance from the content of :obj:`json_path`."""
-        with open(json_path, "r", encoding="utf-8") as f:
-            text = f.read()
-        return cls(**json.loads(text))

src/transformers/training_args.py

@@ -54,7 +54,7 @@ class TrainingArguments:
             :obj:`"no"`.
         do_predict (:obj:`bool`, `optional`, defaults to :obj:`False`):
             Whether to run predictions on the test set or not.
-        evaluation_strategy(:obj:`str` or :class:`~transformers.trainer_utils.EvaluationStrategy`, `optional`, defaults to :obj:`"no"`):
+        evaluation_strategy (:obj:`str` or :class:`~transformers.trainer_utils.EvaluationStrategy`, `optional`, defaults to :obj:`"no"`):
             The evaluation strategy to adopt during training. Possible values are:
 
                 * :obj:`"no"`: No evaluation is done during training.

src/transformers/utils/dummy_pt_objects.py

@@ -1869,19 +1869,10 @@ class MarianTokenizer:
         requires_pytorch(self)
 
 
-class EvalPrediction:
-    def __init__(self, *args, **kwargs):
-        requires_pytorch(self)
-
-
 class Trainer:
     def __init__(self, *args, **kwargs):
         requires_pytorch(self)
 
 
-def set_seed(*args, **kwargs):
-    requires_pytorch(set_seed)
-
-
 def torch_distributed_zero_first(*args, **kwargs):
     requires_pytorch(torch_distributed_zero_first)

tests/test_trainer_callback.py

+import shutil
+import tempfile
+import unittest
+
+from transformers import (
+    DefaultFlowCallback,
+    EvaluationStrategy,
+    PrinterCallback,
+    ProgressCallback,
+    Trainer,
+    TrainerCallback,
+    TrainingArguments,
+    is_torch_available,
+)
+from transformers.testing_utils import require_torch
+
+
+if is_torch_available():
+    from transformers.trainer import DEFAULT_CALLBACKS
+
+    from .test_trainer import RegressionDataset, RegressionModelConfig, RegressionPreTrainedModel
+
+
+class TestTrainerCallback(TrainerCallback):
+    "A callback that registers the events that goes through."
+
+    def __init__(self):
+        self.events = []
+
+    def on_init_end(self, args, state, control, **kwargs):
+        self.events.append("on_init_end")
+
+    def on_train_begin(self, args, state, control, **kwargs):
+        self.events.append("on_train_begin")
+
+    def on_train_end(self, args, state, control, **kwargs):
+        self.events.append("on_train_end")
+
+    def on_epoch_begin(self, args, state, control, **kwargs):
+        self.events.append("on_epoch_begin")
+
+    def on_epoch_end(self, args, state, control, **kwargs):
+        self.events.append("on_epoch_end")
+
+    def on_step_begin(self, args, state, control, **kwargs):
+        self.events.append("on_step_begin")
+
+    def on_step_end(self, args, state, control, **kwargs):
+        self.events.append("on_step_end")
+
+    def on_evaluate(self, args, state, control, **kwargs):
+        self.events.append("on_evaluate")
+
+    def on_save(self, args, state, control, **kwargs):
+        self.events.append("on_save")
+
+    def on_log(self, args, state, control, **kwargs):
+        self.events.append("on_log")
+
+    def on_prediction_step(self, args, state, control, **kwargs):
+        self.events.append("on_prediction_step")
+
+
+@require_torch
+class TrainerCallbackTest(unittest.TestCase):
+    def setUp(self):
+        self.output_dir = tempfile.mkdtemp()
+
+    def tearDown(self):
+        shutil.rmtree(self.output_dir)
+
+    def get_trainer(self, a=0, b=0, train_len=64, eval_len=64, callbacks=None, disable_tqdm=False, **kwargs):
+        # disable_tqdm in TrainingArguments has a flaky default since it depends on the level of logging. We make sure
+        # its set to False since the tests later on depend on its value.
+        train_dataset = RegressionDataset(length=train_len)
+        eval_dataset = RegressionDataset(length=eval_len)
+        config = RegressionModelConfig(a=a, b=b)
+        model = RegressionPreTrainedModel(config)
+
+        args = TrainingArguments(self.output_dir, disable_tqdm=disable_tqdm, **kwargs)
+        return Trainer(
+            model,
+            args,
+            train_dataset=train_dataset,
+            eval_dataset=eval_dataset,
+            callbacks=callbacks,
+        )
+
+    def check_callbacks_equality(self, cbs1, cbs2):
+        self.assertEqual(len(cbs1), len(cbs2))
+
+        # Order doesn't matter
+        cbs1 = list(sorted(cbs1, key=lambda cb: cb.__name__ if isinstance(cb, type) else cb.__class__.__name__))
+        cbs2 = list(sorted(cbs2, key=lambda cb: cb.__name__ if isinstance(cb, type) else cb.__class__.__name__))
+
+        for cb1, cb2 in zip(cbs1, cbs2):
+            if isinstance(cb1, type) and isinstance(cb2, type):
+                self.assertEqual(cb1, cb2)
+            elif isinstance(cb1, type) and not isinstance(cb2, type):
+                self.assertEqual(cb1, cb2.__class__)
+            elif not isinstance(cb1, type) and isinstance(cb2, type):
+                self.assertEqual(cb1.__class__, cb2)
+            else:
+                self.assertEqual(cb1, cb2)
+
+    def get_expected_events(self, trainer):
+        expected_events = ["on_init_end", "on_train_begin"]
+        step = 0
+        train_dl_len = len(trainer.get_eval_dataloader())
+        evaluation_events = ["on_prediction_step"] * len(trainer.get_eval_dataloader()) + ["on_log", "on_evaluate"]
+        for _ in range(trainer.state.num_train_epochs):
+            expected_events.append("on_epoch_begin")
+            for _ in range(train_dl_len):
+                step += 1
+                expected_events += ["on_step_begin", "on_step_end"]
+                if step % trainer.args.logging_steps == 0:
+                    expected_events.append("on_log")
+                if (
+                    trainer.args.evaluation_strategy == EvaluationStrategy.STEPS
+                    and step % trainer.args.eval_steps == 0
+                ):
+                    expected_events += evaluation_events.copy()
+                if step % trainer.args.save_steps == 0:
+                    expected_events.append("on_save")
+            expected_events.append("on_epoch_end")
+            if trainer.args.evaluation_strategy == EvaluationStrategy.EPOCH:
+                expected_events += evaluation_events.copy()
+        expected_events.append("on_train_end")
+        return expected_events
+
+    def test_init_callback(self):
+        trainer = self.get_trainer()
+        expected_callbacks = DEFAULT_CALLBACKS.copy() + [ProgressCallback]
+        self.check_callbacks_equality(trainer.callback_handler.callbacks, expected_callbacks)
+
+        # Callbacks passed at init are added to the default callbacks
+        trainer = self.get_trainer(callbacks=[TestTrainerCallback])
+        expected_callbacks.append(TestTrainerCallback)
+        self.check_callbacks_equality(trainer.callback_handler.callbacks, expected_callbacks)
+
+        # TrainingArguments.disable_tqdm controls if use ProgressCallback or PrinterCallback
+        trainer = self.get_trainer(disable_tqdm=True)
+        expected_callbacks = DEFAULT_CALLBACKS.copy() + [PrinterCallback]
+        self.check_callbacks_equality(trainer.callback_handler.callbacks, expected_callbacks)
+
+    def test_add_remove_callback(self):
+        expected_callbacks = DEFAULT_CALLBACKS.copy() + [ProgressCallback]
+        trainer = self.get_trainer()
+
+        # We can add, pop, or remove by class name
+        trainer.remove_callback(DefaultFlowCallback)
+        expected_callbacks.remove(DefaultFlowCallback)
+        self.check_callbacks_equality(trainer.callback_handler.callbacks, expected_callbacks)
+
+        trainer = self.get_trainer()
+        cb = trainer.pop_callback(DefaultFlowCallback)
+        self.assertEqual(cb.__class__, DefaultFlowCallback)
+        self.check_callbacks_equality(trainer.callback_handler.callbacks, expected_callbacks)
+
+        trainer.add_callback(DefaultFlowCallback)
+        expected_callbacks.insert(0, DefaultFlowCallback)
+        self.check_callbacks_equality(trainer.callback_handler.callbacks, expected_callbacks)
+
+        # We can also add, pop, or remove by instance
+        trainer = self.get_trainer()
+        cb = trainer.callback_handler.callbacks[0]
+        trainer.remove_callback(cb)
+        expected_callbacks.remove(DefaultFlowCallback)
+        self.check_callbacks_equality(trainer.callback_handler.callbacks, expected_callbacks)
+
+        trainer = self.get_trainer()
+        cb1 = trainer.callback_handler.callbacks[0]
+        cb2 = trainer.pop_callback(cb1)
+        self.assertEqual(cb1, cb2)
+        self.check_callbacks_equality(trainer.callback_handler.callbacks, expected_callbacks)
+
+        trainer.add_callback(cb1)
+        expected_callbacks.insert(0, DefaultFlowCallback)
+        self.check_callbacks_equality(trainer.callback_handler.callbacks, expected_callbacks)
+
+    def test_event_flow(self):
+        trainer = self.get_trainer(callbacks=[TestTrainerCallback])
+        trainer.train()
+        events = trainer.callback_handler.callbacks[-2].events
+        self.assertEqual(events, self.get_expected_events(trainer))
+
+        # Independent log/save/eval
+        trainer = self.get_trainer(callbacks=[TestTrainerCallback], logging_steps=5)
+        trainer.train()
+        events = trainer.callback_handler.callbacks[-2].events
+        self.assertEqual(events, self.get_expected_events(trainer))
+
+        trainer = self.get_trainer(callbacks=[TestTrainerCallback], save_steps=5)
+        trainer.train()
+        events = trainer.callback_handler.callbacks[-2].events
+        self.assertEqual(events, self.get_expected_events(trainer))
+
+        trainer = self.get_trainer(callbacks=[TestTrainerCallback], eval_steps=5, evaluation_strategy="steps")
+        trainer.train()
+        events = trainer.callback_handler.callbacks[-2].events
+        self.assertEqual(events, self.get_expected_events(trainer))
+
+        trainer = self.get_trainer(callbacks=[TestTrainerCallback], evaluation_strategy="epoch")
+        trainer.train()
+        events = trainer.callback_handler.callbacks[-2].events
+        self.assertEqual(events, self.get_expected_events(trainer))
+
+        # A bit of everything
+        trainer = self.get_trainer(
+            callbacks=[TestTrainerCallback], logging_steps=3, save_steps=10, eval_steps=5, evaluation_strategy="steps"
+        )
+        trainer.train()
+        events = trainer.callback_handler.callbacks[-2].events
+        self.assertEqual(events, self.get_expected_events(trainer))